What was Reasonable and Prudent?

Basic Rule Speed Restriction

Motorists were to comply with the "basic rule" speed limit when they drove,
in a manner that did not unreasonably endanger other highway users.
To ensure this, drivers were to be constantly alert to changing traffic
conditions and adjust their speed as conditions varied. These conditions
were numerous and could change rapidly. Thus drivers were to be alert for:

the amount and type of traffic sharing the highway with
them. The traffic could have been heavy or light and may have
included trucks, cars, motorhomes, farm equipment, and motorcycles.

changing weather conditions that could have affected driver
visibility and road conditions. These conditions could have included
fog or snow and road surface conditions such as water or ice.

the type of vehicle they were driving, particularly the condition
of their brakes and the weight of their vehicle, which affects
braking ability.

the character of the highway they were driving. Drivers were
to adjust their speed for hills or for winding and narrow roads.

the presence of intersections, railway grade crossings or
pedestrians.

Driving in a careful and prudent manner, complying with the basic rule,
required drivers to be constantly alert and mindful of their personal
responsibility not only for their own safety but also for that of
other highway users.